Since photographic light-sensitive materials are generally composed of an electrically insulating base and photographic layers, static charges are frequently accumulated when the photographic materials are subjected to friction or separation caused by contacting with the surface of the same or different materials during production of the photographic light-sensitive materials or when using them for photographic purposes. These accumulated static charges cause many problems. The most serious problem is discharge of accumulated static charges prior to development processing, by which the light-sensitive emulsion layer is exposed to light to form dot spots or branched or feathery linear specks when development of the photographic films is carried out. This phenomenon is the so-called static mark, by which a commercial value of the photographic films significantly deteriorates, and is sometimes entirely lost. For example, in the case of medical or industrial X-ray films, it is easily understood that the static marks may result in a very dangerous judgment or misdiagnosis. This phenomenon is a very troublesome problem, because it becomes clear for the first time by carrying out development. Further, these accumulated static charges are also the origin of secondary problems such as adhesion of dusts to the surface of films, uneven coating, etc.
As described above, such static charges are frequently accumulated in the cases of producing and using photographic light-sensitive materials. For example, in production, they are generated by friction of the photographic film contacting a roller or by separation of the emulsion face from the base face during rolling or unrolling. Further, they are generated on X-ray films in an automatic camera by contacting with or separating from mechanical parts or fluorescent sensitizing paper, or they are generated by contact with or separation from rollers and bars made of rubber, metal, or plastics in a bonding machine or an automatic developing machine in the developing shop or in a camera in the case of using color negative films or color reversal films. In addition, they are generated by contact with packing materials, etc.
Static marks on photographic light-sensitive materials occurring due to accumulation and discharge of static charges increase with increases in the sensitivity of the photographic light-sensitive materials and an increase of the processing speed. Particularly, static marks are easily generated because of high sensitization of the photographic light-sensitive materials and severe processing conditions such as high speed coating, high speed photographing, and high speed automatic processing.
In order to prevent these troubles caused by static charges, it is suitable to add antistatic agents to the photographic light-sensitive materials. However, antistatic agents used conventionally in other fields cannot be used freely for photographic light-sensitive materials, because they are subjected to various specific restrictions due to the nature of the photographic light-sensitive materials. More specifically, it is required for the antistatic agents capable of use in the photographic light-sensitive materials that not only is the antistatic ability excellent, but also that they do not have an adverse influence upon photographic properties of the photographic light-sensitive materials, such as sensitivity, fog, granularity, sharpness, etc., that they do not have an adverse influence upon film strength of the photographic light-sensitive materials (namely, that the photographic light-sensitive materials are not easily injured by friction or scratching), that they do not have an adverse influence upon adhesion resistance (namely, that the photographic light-sensitive materials do not easily adhere when the surfaces of them are brought into contact with each other or with surfaces of other materials), that they do not accelerate deterioration of processing solutions for the photographic light-sensitive materials, and that they do not deteriorate adhesive strength between layers composing the photographic light-sensitive materials, etc. Accordingly, applications of antistatic agents to photographic light-sensitive materials are subject to many restrictions.
One method for overcoming problems caused by static charges comprises increasing electric conductivity of the surface of the photographic light-sensitive materials so that static charges disappear within a short time, prior to spark discharging of the accumulated charges.
Accordingly, processes for improving the electrically conductive property of the support or the surface of various coating layers in the photographic light-sensitive materials have been proposed hitherto, and utilization of various hygroscopic substances, watersoluble inorganic salts, certain kinds of surface active agents and polymers, etc., has been attempted. For example, it has been known to use polymers as described in U.S. Pat. Nos. 2,882,157, 2,972,535, 3,062,785, 3,262,807, 3,514,291, 3,615,531, 3,753,716, 3,938,999, etc., surface active agents as described in U.S. Pat. Nos. 2,982,651, 3,428,456, 3,457,076, 3,454,625, 3,552,972, 3,655,387, etc., and metal oxides and colloidal silica as described in U.S. Pat. Nos. 3,062,700, 3,245,833, 3,525,621, etc.
However, many of these substances exhibit great specificity, depending upon the kind of film support or the photographic composition, and there are cases that, although they produce a good result on certain specific film supports, photographic emulsions or other photographic constituting elements, they are not only useless for improving antistatic property in case of using different film supports and photographic constituting elements, but also have an adverse influence upon photographic properties.
On the other hand, there are many cases wherein, although they have excellent antistatic effects, they cannot be used because of having an adverse influence upon photographic properties such as sensitivity, fog, granularity, sharpness, etc. For example, it has been well known that polyethylene oxide compounds have antistatic effects, but they often have an adverse influence upon photographic properties, such as increasing fog, desensitization, deterioration of granularity, etc. Particularly, in light-sensitive materials in which both sides of the base are coated with photographic emulsions, such as medical direct X-ray light-sensitive materials, it has been difficult to develop techniques for effectively providing an antistatic property without having an adverse influence upon photographic properties. Thus, the application of antistatic agents to the photographic light-sensitive materials is very difficult, and their use is often limited to a certain range.
Another method for overcoming the problems of photographic light-sensitive materials caused by static charges is that which comprises controlling the triboelectric series of the surface of the light-sensitive materials to reduce generation of static charges caused by friction or contact as described above.
For example, it has been attempted to utilize fluorine containing surface active agents, as described in British patents 1,330,356 and 1,524,631, U.S. Pat. Nos. 3,666,478 and 3,589,906, Japanese patent publication No. 26687/77 and Japanese patent application (OPI) Nos. 46733/74 and 32322/76 (the term "OPI" as used herein refers to a "published unexamined Japanese patent application"), etc., for photographic light-sensitive materials for the above-described purpose.
However, photographic light-sensitive materials containing these fluorine containing surface active agents generally have an electrostatic property of charging in negative polarity. Accordingly, although it is possible to adapt the triboelectric series of the surface of the light-sensitive materials for each triboelectric series of rubber rollers, Delrin rollers and nylon rollers by suitably combining the fluorine containing surface active agents with coating aids having an electrostatic property of charging in positive polarity, problems still occur. That is, when such prior fluorine containing surface active agents are used so as to adapt for rubber, branched static marks occur due to Delrin, of which triboelectric series is situated on the positive side comparing to the triboelectric series of rubber; and when they are used so as to adapt for Delrin, spot static marks occur due to the rubber, of which triboelectric series is situated on the negative side comparing to the triboelectric series of Delrin. In order to compensate for these problems, a method for reducing the surface resistivity using high molecular weight electrolytes together with the fluorine containing surface active agents is known. However, such a method brings about various evil effects, for example, an adverse influence upon adhesion resistance, an adverse influence upon photographic properties. Therefore, it is impossible that these compounds are incorporated into photographic light-sensitive materials to the extent of obtaining sufficient antistatic properties.
Still another method for preventing the occurrence of static marks is that in which ultraviolet ray absorbing agents are employed. It has been known that a distribution of spectral energy of discharge luminescence which causes static marks is in a range of 200 nm to 500 nm and, particularly, the intensity thereof is high in a range of 300 nm to 400 nm, and light energy in this range causes occurrence of static marks. Accordingly, attempts have been made to prevent the occurrence of static marks by shielding ultraviolet rays in a range of 300 to 400 nm by means of ultraviolet ray absorbing agents, as described in, for example, Japanese patent publication No. 10726/75, Japanese patent ppplication (OPI) No. 26021/76, French patent 2,036,679, etc.
Usually, color photographic light-sensitive materials free from the occurrence of static marks are produced by means of a combination use of the above-described methods. Of these methods, a method in which fluorine containing cationic surface active agents an antistatic property of which is less dependent on the materials are used together with ultraviolet ray absorbing agents in the side of silver halide emulsion layer or in a gelatin back layer is particularly effective. However, it has been found that while this method brings remarkable improvements in antistatic property, characteristics of the photographic light-sensitive material with respect to pressure are seriously degraded.